1. Field of the Invention
The present invention relates to a lawn mower control system.
2. Description of the Related Art
Lawn mowers are commonly equipped with a grass bag, in which the grass cut by a grass-cutting blade is collected. When the grass bag is filled up with cut grass, the rotation of the blade meets with resistance and the load on the engine for driving the blade increases. Therefore, the engine speed decreases in a lawn mower wherein the engine speed is adjusted with a mechanical governor, and it is possible for the operator to know thereby that the grass bag has become full.
However, in a lawn mower equipped with a so-called electronic governor that opens and closes a throttle valve with an actuator to adjust the engine speed, the throttle opening is adjusted so as to maintain the desired speed even if the engine load increases, so the engine speed does not decrease, and therefore the operator cannot physically sense that the grass bag has become full. When the lawn mower continues to operate with a full grass bag, the engine is subjected to an excessive load, which results in the occurrence of stalls, the clogging of the space between the blade and the blade housing with cut grass, and other such drawbacks.
In view of this, a lawn mower based on the technology described in Japanese Laid-Open Patent Application No. 5-76232, for example, is configured such that an optical sensor is mounted near the opening of the grass bag, it is determined that the grass bag has become full when light is blocked by the accumulated grass near the opening, and the operator is informed by a buzzer or a lamp. The lawn mower according to Japanese Laid-Open Patent Application No. 5-76232 is a riding lawn mower.
However, providing a dedicated sensor for detecting that the grass bag is full as described above has drawbacks in that space is needed for mounting the sensor, and the cost increases. In a non-riding lawn mower requiring small size and low cost, the drawbacks are particularly significant and installing a dedicated sensor has been difficult.
Also well known is a technique whereby a grass-cutting blade is driven by a mounted engine, and the wheels are driven to allow the lawn mower to be self-propelled. When the blade and wheels are driven, the engine speed must be increased to be higher than the idling engine speed because of the increased load. However, the engine speed is adjusted manually in many conventional lawn mowers, so it has been troublesome to adjust the engine speed according to the driving of the blade or wheels. Consequently, in many cases the engine speed is continuously kept at a level above the idling speed, at which an output sufficient to drive the blade or wheels is generated, creating drawbacks such as reduced fuel efficiency and increased noise.
In view of this, the technique described, for example, in Japanese Laid-Open Patent Application No. 5-147460 (paragraph 0005, etc) has been proposed. According to this technique, a riding lawn mower is configured such that a pressure sensor detects that the rider is sitting, the transmission is brought to the forward-movement position, the engine speed is immediately increased to the maximum speed when the PTO clutch is detected to have been engaged (in other words, when grass is being cut while the lawn mower is moving), and the engine speed is maintained at idling speed when any of the above-mentioned conditions are not met.
In a non-riding lawn mower, sometimes only the blade is driven to perform the cutting operation (the wheels are not driven and the mower is pushed manually) when grass is cut over a small area and in other situations. Also, sometimes the blade is not driven and only the wheels are driven in a self-propelling mode in order to reduce the load for moving the lawn mower. However, the aforesaid prior art (5-147460) does not go so far as to separately consider the driving of the wheels and the driving of the blade and to vary the engine speed accordingly, thus leaving room for improvement in terms of operability.
Also, if the engine speed is immediately increased to the desired (maximum) speed under the right conditions, the lawn mower may suddenly accelerate and become less maneuverable, as described in the aforesaid prior art (5-147460).